The present invention relates primarily to a knee airbag module which is integrated into a dashboard (a/k/a instrument panel) or into the transition area between the dashboard and footwell cover in a motor vehicle interior. In principle, however, the concept according to the invention can also be used in other airbag modules, for example side impact airbag modules.
Such an airbag module generally incorporates an essentially rigid housing with an outlet opening, an airbag folded into the housing, an inflator having at least one outflow opening, generally multiple outflow openings, of which at least one outflow opening is located within the airbag, and a covering element which covers the outlet opening of the housing.
A generic airbag module, namely a knee airbag module, is described in U.S. Pat. No. 7,261,314. Here, alongside the housing base, the housing has a wall which extends from the housing base and which defines the outlet opening of the housing. The wall extending from the base is designed as a fully circumferential wall with a first wall section, namely the vehicle rear wall section, a second wall section, namely the vehicle front wall section, and two side sections which are also designated as the third and fourth wall sections. Here, the edge of the first wall section running essentially parallel to the outlet opening has a slot-shaped receptacle, which can also be designated as a mounting groove. This receptacle is used to mount an end section of the covering element.
The covering element is an injection molded element formed in one piece and can be described as having three functional sections. These three functional sections are the first end section just referred to, the main section which spans the outlet opening and which is designed to be essentially on one plane, and a second end section which is used to attach the covering element to the second wall section, so to the vehicle front section. Here, the first end section is designed in two parts, namely bifurcated, and one part of the first end section extends into the slot-shaped receptacle in which it is clamped in place.
When the gas generator is activated and the airbag inside the airbag module begins to expand, the airbag, i.e. the prevailing gas pressure therein, pushes the part of the first section of the covering element which was originally located in the receptacle out of the receptacle and the covering element, under deformation, at least partially frees up the outlet opening so that the airbag can escape through it.
For practically all components in a present day motor vehicle, even for the airbag modules installed in the motor vehicle, there is a general desire to design them to be as light as possible, so with a low mass, while fully preserving their functionality. The heaviest components in an airbag module, in particular an airbag module as set out above, are generally the housing and the inflator, usually designed as a gas generator. Particularly in knee airbag modules, this results in the following feature: owing to the distance between the occupant knee/shin area and the dashboard, which is generally very small, and owing to the fact that a knee airbag should be effective in particular for vehicle occupants not wearing a seatbelt, there is very little time between the point in time when the gas generator receives the initiation signal and the time at which the knee airbag should be fully unfolded and deployed.